Retractable awning structures in which the awning is mounted in a frame, housing or box find wide spread commercial utility for use on recreational vehicles as well as on permanent structures. Such retractable awning assemblies conventionally include a closable housing or box adapted to be mounted upon a wall such as a wall of a recreational vehicle, a building structure, or the like, and a flexible sheet of awning material which can be rolled up and stored within the housing or pulled out to a extended awning position. The awning, when extended, is supported by an appropriate brace structure, and the brace members are conventionally housed within the box or housing when the awning is in a stored position. Awnings of this type are shown in copending U.S. patent application of Donald S. McKee, Ser. No. 522,640, filed Nov. 11, 1974, for "Enclosable Retractable Awnings"; U.S. Pat. No. 3,364,973, issued Jan. 23, 1968, to R. E. Railson for "Retractable Awning"; and U.S. Pat. No. 3,833,011, issued Sept. 3, 1974, to D. D. Duffy for "Retractable Awning Assembly." Such awning structures are readily mountable upon vertical walls, such as the side wall of a trailer, camper or other recreational vehicle, by fastening the awning housing or frame directly to the wall. Problems are encountered, however, in the case of many recreational vehicles, such as trailers, which have convexly curved walls of such configuration that a planar vertical surface is not available for mounting the awning structure. Because of the wide variety of recreational vehicle configurations, the possible wall curvature configurations on which awnings are to be mounted varies widely.